Electrical device, method and material



March 5, 1968 J YD ET AL ELECTRICAL DEVICE, METHOD AND MATERIAL FiledDec. 18, 1963 WA w m w m o h F mi 4 v R\ Q W/ H/ mum G r m F .6 GRAMS 0FDISPERSING AGENT FIG. 3

INVENTORS JAMES R. BOYD CRYSTALLITE SIZE fi am; ANGSTROMS ATTORNEYUnited States Patent Office 3,372,058 Patented Mar. 5, 1968 3,372,058ELECTRICAL DEVICE, METHOD AND MATERIAL James R. Boyd, Austin, Tex., andArthur H. Mones, Poughkeepsie, and John C. Schottmiller, Penfield, N.Y.,assignors to International Business Machines Corporation, New York,N.Y., a corporation of New York Filed Dec. 18, 1963, Ser. No. 331,534 11Claims. (Cl. 117-227) ABSTRACT OF THE DISCLOSURE Metal glaze resistivecompositions suitable for application to a ceramic dielectric comprising15 to 70% of a palladium or rhodium oxide having a crystallite size witha surface area of at least 0.75 m. gm. and up to 35% of a conductivemetal dispersed in a glass matrix comprising 35 to 70% vitreous enamelfrit.

This invention relates to metal glaze resistors, and, in particular, tometal glaze resistive compositions, to the method of fabricating metalglaze resistors, and to the metal glaze resistors produced therefrom.

The present trend toward microminiaturization has focused attention onmetal glaze resistors as components of integrated electronic circuits.Made from mixtures of glass and noble metal powders, these metal glazeresistors offer Wide resistance ranges, flexibility in their processing,product versatility, economy and performance capabilities not availablewith other conventional resistors.

Of these metal glaze resistors, palladium-glass andpalladium-silver-glass systems potentially offer rather desirablecharacteristics. These resistors are formed by combining glass,palladium and silver powders of small particle size and uniformlydispersing the mixture in an organic vehicle, the organic vehicle beingchosen in some instances for its high boiling point and in others forthe flow properties that it imparts to the dispersion. Through variationof the organic vehicle, metal glaze coatings are applied to almost anysubstrate configuration by methods such as screening, spraying, dippingor transfer wheel systems. Once applied to the substrate, the vehicle isvolatilized at about 100 C. and the material is fired at a temperaturewhich ranges between 750 C. to 850 C. to melt the glass and to suspendthe metal' constituents in a fixed relationship, one to the other.

Although the palladium-glass and the palladium-silverglass metal glazeresistors offer advantages not available with other types of resistors,they are not altogether satisfactory in providing stability, uniformityand reproducibility of electrical characteristics at commerciallyacceptable yields. Drift and wide scattering in the resistance andtemperature coefficient of resistivity (hereafter designated TCR) areexperienced in preparing these metal glaze resistors. Particularly, whenrigid end of life specifications are required for all circuit componentsto perform satisfactorily. The appearance of any of these aforementionedadverse phenomena upsets the electrical balance required for successfuloperation of the circuits. Accordingly, it has been an object ofconsiderable research to find metal glaze resistors having stableelectrical characteristics With a reproducibility factor at commerciallyacceptable yields.

It is an object of this invention to provide an improved metal glazeresistor having stable electrical resistance and temperature coefficientof resistivity.

It is another object of this invention to provide a metal glaze resistorcomposition having enhanced electrical characteristics and uniformity inperformance.

It is yet another object of this invention to provide an improved methodfor producing metal-glaze resistors.

It is a further object of this invention to provide an economicallyfeasible method for producing metal glaze resistors having productversatility and uniformity in performance characteristics.

Resistive metal glazes of this invention are formed by combiningvitreous enamel frit with palladium or rhodium and thereafter firing thecompact to produce a material having a microstructure which ischaracterized by a dispersion of metal oxide and metal in a glassmatrix. To modify properties such as thermal stability, a conductivecomponent such as silver is added to the vitreous enamelpalladium oxidereaction mixture. The silver serves to modify the oxidation reactionpromoted during the firing process but the amount admissible to thereaction product is limited, since silver, when an electric field isapplied, tends to migrate which results in variations in resistivity.Large amounts of silver also leads to poor reproducibility inresistivity because, presumably, of inconsistent silver linkages inparallel with the resistive phase of palladium oxide. What has beendiscovered is that stability and uniformity in electricalcharacteristics are achieved, when the palladium and rhodium, or theiroxide, added to the reaction mixture, are maintained within selectedcrystallite sizes or surface areas. This is most surprising since it waspreviously thought that it was the size of the palladiu-m or oxideparticle, a particle being defined as an agglomerate of crystallites,that exerts the influence on the resulting electrical characteristics;it was felt that it was only necessary to maintain palladium or itsoxide particle to a size of less than 325 mesh, and, preferably to asize between 0.1 and 50 microns. It has been found that problems stillexist with stability, reproducibility and uniformity in the desiredelectrical characteristics where selection of palladium or rhodium ortheir oxides are based solely on particle size. On the other hand,maintaining the crystallite size of the palladium to below 1500Angstroms, and preferably to less than 1000 Angstroms, providesstability, uniformity and reproducibility in the resistive metal glazes.With extremely large crystallite sizes, that is, with those that exceed1000 to 1500 Angstroms, oxidation becomes sluggish and it becomesdifficult to assure the presence of a highly dispersed oxide phase inthe resistor. Palladium crystallites within the selected valuescorrespond (after sintering) to palladium oxide crystallites withsurface areas of at least 0.75 m. gm. to 1.5 m. /gm., with it beingpreferable to use crystallites with a surface area of about 1 m. gm.

The significance of crystallite size is particularly evident in thepreparation of loW resistivity material, that is, material having asheet resistivity of about ohms per square. Low resistivity material maybe prepared by: 1) increasing the silver concentration; (2) decreasingthe glass concentration; (3) doping the resistor with, for example, thecation lithium. The last of these techniques is the subject of copendingUS. patent application Ser. No. 313,032, filed in behalf of Arthur H.Mones and Kenneth E. Neisser, Jr., and which is assigned to the assigneeof the instant application. Increasing silver to levels Where the silverto palladium cation ratio is greater than about 1.5 results in poorreproducibility, extremely high positive TCRs and load instability whichare due presumably to silver migration. Decreasing the glassconcentration to levels much below 35 percent results in reducedmoisture stability. Doping with lithium, for example, to produceresistivities of the order of 100 ohms per square usually results inhigh positive TCRs.

The effect of crystallite size (or surface area) on resistivity and TCRis brought out by Table I below. The first two columns in the table givethe crystallite size as based on X-ray diffraction data along thecrystal directions as specified. The third column presents surf-ace areameasurements which are in meters square per gram of material. The fourthcolumn in the table presents the particle size which is determined bythe usual techniques of sedimentation and screening procedures. The lasttwo columns in the table present resistivity in ohms per square and TCRin parts per million per degree (p.p.rn./ C.). What is observed from thetable is that there is a relationship between crystallite size orsurface area with resistivity and TCR, whereas a relationship is lackingbetween particle size and the electrical characteristics. The data ispresented for fixed glass and silver concentration, the crystallite sizeof silver is also fixed and has a similar affect on the electricalcharacteristics.

Uniformity of resistivity is not achieved through particle sizeselection as was previously thought. This is further emphasized in TableII below where particle size is varied while crystallite size as basedon, in this case, surface area of the palladium oxide is maintainedconstant at about 1 m. gr.

TABLE II Particle Size, Resistivity, ohms per TCR, p.p.rn./ 0.

microns square (ZS-100 C.)

It will be recognized by those skilled in the art that wherever silveris used as a conductive component it is replaceable wholly or partiallywith either gold or platinum or both with substantially similar results,and, where palladium or palladium oxide is contemplated, it isreplaceable wholly or partially by rhodium or rhodium oxide.

Further beneficial effects are available with the addition of smallamounts of dispersing agents. The addition of oxides such as siliconoxide and alumina into the initial reaction product enables thefabrication of resistors with still further improvements inreproducibility and enables reduction in TCR without substantiallyaffecting resistivity.

The crystallites used in the initial reaction mixture are formed bytreating palladium powder in a furnace under non-oxidizing conditionswhere the palladium power grows into crystallites of a desired size.They are then removed and oxidized at a temperature maintained between750 C. to 800 C. for approximately 2 hours to convert the palladium tothe oxide.

It is important that the crystallites incorporated into the initialreaction product undergo sintering prior to oxidation, sintering beingdefined as that process where the palladium grows into largercrystallites. If, for example, palladium black of arbitrary crystallitesize is oxidized and the sintering step bypassed, the resistivityobtained in the end product lacks the reproducibility, uniformity andstability as that obtained with the sintered palladium crystallites ofcontrolled size. The reasons for this are not really known but a workinghypothesis has been formulated, namely, that electrical linkagescomposed of large crystallites as opposed to small crystallites for afixed distance will have lower resistivity by virtue of having lessgrain boundary contacts. In the limiting case a single crystal will haveminimum resistivity. It is important therefore to control thecrystallite size for uniformity in resistivity and enhancement of otherproperties.

The reasons for conversion to oxide are: (1) finely di- 4. videdpalladium tends to sinter in mixing operations whereas palladium oxidedoes not, and (2) finely divided palladium tends to catalytically affectthe organic vehicle whereas palladium oxide does not. Uniformity andshelf life are enhanced by conversion to oxide.

The palladium crystallites are combined with silver, gold and platinum,dispersing agent, and organic vehicle, coated on a substrate and thereaction mixture fired in an oxidizing atmosphere to temperatures up to750 C. Although it is usually not desirable to have the firingtemperature exceed 790 C. for prolonged periods, since the palladiumoxide tends to reconvert to palladium metal, a condition which hasdeleterious if not completely disastrous effects on the operation of theresistive metal glaze, still further improvement is achieved if thefiring temperature is allowed to exceed 850 C. under particularconditions.

To take advantage of this high temperature firing, the palladium oxide,silver and vitreous enamel are mixed as previously. The compact is firedat 850 C. to decompose the palladium oxide to form a palladium-silveralloy. The reaction product is then refired at temperatures in the rangebetween 450 C. to 750 C. to yield a product with a further degree ofsensitivity than available from the low temperature firing. Anadditional advantage of the high temperature firing is that vitreousenamel frits that include glass that softens at temperatures above 800C. are usable, thereby overcoming a limitation of the low temperaturefiring process. Additionally, with the palladium oxide and glass systemfiring the initial reaction product at temperatures exceeding 750 C.enhances the drift characteristics markedly over those observed withmetal glaze resistive materials fired at temperatures of less than 750C.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention as illustrated inthe accompanying drawings.

In the drawings:

FIGURE 1 is a sectional view to a greatly enlarged scale of a portion ofan electrical resistance element in accordance with the presentinvention;

FIGURE 2 is a graph of resistivity and TCR versus grams of dispersingagent for a palladium oxide silver glass composition;

FIGURE 3 is a plot of resistivity per square for a palladium oxide,silver and glass composition versus crystallite size.

A metal glaze resistor element 10 in accordance with the persentinvention includes an electrically nonconducting base 11 of a suitablematerial such as a ceramic having fired thereon a thin layer 12 of aparticular resistive metal glaze. The resistance composition includes aquantity of finely divided material from the group consisting ofpalladium oxide 13 and rhodium oxide. In addition the glaze includesdivided glass 14 which may be lead borosilicate or the like and, inaddition, the glass may also include a finely divided conductivematerial of noble metal, i.e., silver, gold, or platinum, which aids inadjusting the resistivity of the final resistor element.

Speaking more particularly now, resistive metal glaze compositions areformed for application as resistors with a microstructure that containsa dispersion of palladium oxide and silver-palladium or palladium phasesin a matrix of glass. Wherever silver is used, it is replaceable whollyor partially with either gold or platinum or both with substantiallysimilar effects in the microstructure and, where palladium or palladiumoxide is contemplated, it is replaceable wholly or partially by rhodiumor rhodium oxide, the replacement, of course, being based on equivalentamounts. The initial reaction mixture includes 35% to 70% by weightvitreous enamel frit and 15% to 70% by weight sintered palladium oxide,with a palladium crystallite size up to 1500 Angstroms, and preferablyup to 1000 Angstroms, which corresponds to a palladium oxide crystallitewith a surface area of at least 0.75 mF/gm. to 1.5 m. /gm. andpreferably 1 m. gm. Where silver is a component of the initial reactionmixture, it may constitute up to 35% by weight of reaction mixture withthe cation ratio of the silver to palladium maintained between 0.5 to1.5. The preferred composition for a resistor includes 60% by weightvitreous enamel frit with the balance being silver and palladium, thesilver being present up to 22% by weight and the palladium being presentin the range between 18% to 60% by weight, with a silver to palladiumcation ratio between about 0.9 to 1. The TCR of such a material isreducible to zero p.p.m./ C. (ZS-100 C.) and has optimum load andmoisture stability characteristics. Typical formulations with theresulting electrical characteristics are illustrated in Table III.

The additions of inert oxides are eifective in altering TCR only whensize is in colloidal range. Large crystallite sizes, for example,greater than 27 microns, appear 5 only to dilute the system which bringsabout an increase in resistivity.

TABLE III Yield 530% Percent R Av. 500 Percent R Example Ratio Ag/PdGlass Cone, R/K-ohms TCR, p.p.m./ Resistors to hrs., w./sq. inch, Av.1,000 hrs., Surface Area,

Percent 0. Nominal Value 60 0., in 90% RH same condition mJ/gm.

Circuit Bias 5 45 0. 9 70% 54 53 21 5 70 25 1, 000 70% 69 +1. 48 21 1. 057. 3 1. 5 175 53% 33 41 21 1. 0 57. 3 1.5 161 84% 28 36 21 1. 5 70 0.151, 000 60% -13. 8 26 21 0. 9 60 3 5:100 70% +0.17 +0.18 21 1. 1 60 0.12+350 70% 0. 40 0. 41 1. 8

The table illustrates the significance of utilizing crystallite sizes orsurface areas of selective values to achieve uniformity, reproducibilityand stability in the electrical characteristics as opposed to theprevious techniques of composition adjustments including those ofparticle size. In this manner compositional ranges are availableyielding optimum characteristics, for example, in TCR drift andreproducibility. Increasing silver as illustrated in Example E toproduce low resistivity material does not produce as a stable result incomparison to Example G where crystallite size or surface is variedwithin selected values to achieve a lower resistivity which isaccompanied by additional desirable properties.

Returning now to Table III, a brief explanation may further enhance whatis illustrated. The first two columns present the composition of theresistive metal glaze, the glass being given in Weight percent. Takingthe weight percent of glass from 100 percent yields the amount of otherconstituents in the initial reaction mix. For example, where the glasscomprises 45% by weight and the silver and palladium are present with acation ratio of about 0.5, the silver constitutes about 18% and thepalladium about 38% of the initial reaction mixture. The third andfourth columns present the resistance per square in kilo ohms and TCR inp.p.m./ C. The fifth column indicates the yield obtained with thetechniques of the present invention. The data presented, for Example E,is for yields of 115%. The next to the last two columns presentstability characteristics, that is, the change in resistance overperiods of 500 and 1000 hours where tests are conducted with theapplication of 15 watts per square inch at 60 C. at 90% relativehumidity with the circuit biased. The eifect of crystallite size on theelectrical characteristics is graphically illustrated in FIG. 3 of thedrawings.

Additional improvements with the electrical characteristics of theresistive metal glaze are achieved with the addition of up to about 5%of dispersing agent where the dispersing agent is selected from thegroup consisting of silicon or aluminum oxide or their equivalents. Theeffect of these dispersing agents on the electrical characteristics isgraphically illustrated in FIG. 2 of the drawings. Further, theadditional beneficial elfects of the dispersing agents are given inTable IV.

TABLE V Temperature, C. Soak Time, Minutes Best Value For CrystalteSize, Angstrom Units Room Temperature 189 285 .15 336 205 60 460 335 15432 335 60 641 385 15 606 385 30 779 440 15 1, 056 440 60 1, 072 466 151, 090 466 60 1, 488 488 30 1, 635 514 15 1, 556 514 30 1, 815

To avoid oxygen contamination during the treatment of the palladiumpowder, the palladium powder is heated in a forming gas atmosphere. Ifthe hydride is formed as a result of this treatment, the palladium isthen treated in a vacuum for 2 hours at C. to decompose the hydrideproduced from the forming gas treatment. The palladium crystallites arethen inserted in a furnace containing an oxidizing atmosphere maintainedat a temperature of about 750 C. for about 2 hours where the palladiumforms palladium oxide of the desired crystallite size. Any sinteringtemperature and time may be used provided it furnishes a substantiallypure palladium oxide crystallite without a metal phase.

Although there is no lower limit for the crystallite size of thepalladium save that which is producible from the process, the upperlimit for the crystallite size is about 1500 Angstroms and preferablyabout 1000 Angstroms. This corresponds to palladium oxide crystalliteswith a surface area of at least 0.75 m. /gm., and, preferably at least 1m. /gm. Where crystallites exceeding 1500 Angstroms are used, widescatterings and poor scaling is achieved with the electricalcharacteristics. Accordingly, it is preferable to maintain the palladiumcrystallite size to less than 1500 Angstroms. After the crystallites ofdesired size are prepared they are combined with vitreous enamel frit,the frit used may be composed of glass frit such as borosilicate frit,lead borosilicate frit, or other borosilicate frit, the preparation ofthese being well known in the art. The vitreous enamel frit, the metaloxide powders, with or without silver being present, and the colloidaldispersing agent are milled for about 2 hours. The mixture is thencombined with a vehicle which is in the form of a liquid or paste. Anyinert liquid may be employed for the purpose, for example, water,organic solvent with or without thickening agents, stabilizing agents,or the like, all of which are well known in the art.

Preferably the dispersing agents such as silicon oxide or aluminum oxideadded to the initial reaction mixture are maintained below a particlesize of about 5 microns. The effect of the addition of dispersing agentis most pronouncedit acts to decrease the TCR. For example, in aresistive composition having initial resistivity of 2850 ohms per squareand a TCR of +100 p.p.m./ C., the

addition of 1.6% to 4% by weight of dispersing agent brings about a31.6% change in resistivity; it changes the resistivity to 3750 ohms persquare while changing the TCR to about 100 p.p.m./ C.

After the initial reaction mixture is prepared, it is applied to adielectric substrate capable of withstanding the firing temperature ofthe vitreous enamel palladium oxide metal composition. The substrate maybe alumina, for example, glass, porcelain, refractory barium titanate orthe like, preferably the ceramic substrate should have a smooth,substantially uniform surface. The initial re action mixture is appliedin thickness to the order of about 0.001 inch. After application on thedielectric substrate, the substrate and mix coated thereon is insertedin an oxidizing atmosphere and fired at a temperature between 700 C. and790 C. for periods of a few minutes to several hours and preferably forabout 20 minutes. In this manner glaze resistors are formed having thedesired electrical characteristics.

As previously brought out, the initial reaction mixture of the instantinvention includes 35% to 70% by weight vitreous enamel frit with thebalance being palladium or palladium oxide with a crystallite size up to1500 Angstroms. Where silver is also incorporated into the reactionproduct the cation ratio is maintained between 0.5 to 1.5, andpreferably between 0.9 to 1.1. The operable and preferred ranges for theinitial reaction product are presented in Table VI in weight percent.

TABLE VI Ingredients Percent Operable Percent Preferred Example 1Starting with palladium with a surface area of 2.1 m. /gm., the materialis heated in forming gas at a temperature of 440 C. for 1 hour. Thetreated palladium has a surface area of 1.8 m. gm. This material isoxidized at 750 C. in oxygen for 2 hours. The resultant oxide has asurface area of 1 m. /grn.

21% by weight silver 19% by weight palladium oxide 60% by weight glassAg/Pd: 1.1

To this mixture 'isadded finely divided colloidal silica such that theratio is 1.5% colloidal silica to 98.5% of the above mixture. The solidsare thoroughly mixed in'a high speed shaker for aboutZ hours. A vehicle,for example, beta terpineol, isadded to the solids and the solidsarethoroughly wet. Conventional milling equipment is used. Solidconcentration is 80%. The mixture which is suitable for screening isdeposited in 1 mil layers to a stencil on ceramic, typically 96%alumina. The deposited composition is dried at about 100 C. and theceramic with deposit is fired at about 750 C. for about 20 minutes.Resistivities from 'such a mixture are about 100 ohms per square and theTCR about +300 parts per million per C.

Example 2 21% palladium oxide 19% silver 60% glass Ag/Pd=0.9

' Colloidal silica is added to represent 1.5% of the total solids. Thecompact is mixed and wetted as described in Example 1, similarly screendeposition and firing is performed as in Example 1. Resistivity istypically 3000 ohms per square accompanied by a TCR of about p.p.m./C.

Values for resistivity and TCR may be varied by various techniques andmaterials. It is known that changes in detail and purity of rawmaterials, wetting, mixing, dispersion, and firing techniques will alterresistivity and TCR. The methods and materials must be consistent andcarefully controlled to realize good reproducibility any good mixing andwetting techniques are usable provided they are consistently followed.

To obtain the additional improvements available with the metal glazeresistors, when the mix constitutes palladium oxide and vitreous frit,the initial reaction mix is fired at temperatures that exceed 790 C.Drift characteristics are further enhanced in this manner. The procedureis illustrated in Example 3 below.

Example 3 A reaction mix constituting 45% by weight palladium oxide withthe balance glass is prepared as in Example 1. After deposition on aceramic surface, the mix is fired in an air atmosphere at about 850 C.for a selected period of time which may be as short as several minutes.The reaction mix is then quenched to room temperature in about 2%minutes to minimize reoxidation of the palladium. The mix exhibits aresistivity of about 4000 ohms per square and a TCR of about 220p.p.m./C. and has drift characteristics which are maintained to withinabout 2% to 3% under accelerated stress conditions, that is, 250 C. for16 hours. I

Where the reaction mix includes a conductive component, the hightemperature firing requires an additional step. The reaction mixture isinitially heated to a temperature of about 850 C. to decompose thepalladium oxide to form a palladium-silver alloy. Following this, it isreoxidized at a temperature in the range between 450 C. to 700 C. toform selected amounts of palladium oxide. The procedure is illustratedin Example 4.

Example 4 A reaction mix is prepared containing 16.8% palladium, 23.2%silver, with the balance glass. The details of preparation are similarto those previously described. After screening on a ceramic substrate,the mix is fired at 850 C. for 20 minutes. X-ray diffraction analysisindicated that the palladium oxide decomposed and had a resultantresistivity of 1.5 ohms per square. The reaction product was thenreoxidized at 650 C. for periods varying between 48 hours to 160 hours.Under these conditions the resistivities, as desired, are achievedbetween 223 to 3000 ohms per square.

What has been described are resistive metal glazes having outstandingelectrical characteristics which are reproducible at commerciallyacceptable yields. These metal glaze resistors are characterized by amicrostructure having a metal oxide and metal phase dispersed in a glassmatrix. Through the regulation of the crystallite size, of the addedconstituents, wide range of electrical characteristics are-availablewith given compositional systems. In addition, these results areavailable through processing procedures that maintain the requiredcompositional balance between metal and metal oxide phases in thedispersed glass matrix.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

What is claimed is:

1. A metal glaze resistive composition adapted to be applied to andfired on a ceramic dielectric characterized by a microstructure having adispersion of metal oxide and metal in a glass matrix where the initialreaction mix for said metal glaze resistive composition includes:

35% to 70% by weight of vitreous enamel frit;

15% to 70% by Weight of particles comprising agglomerates ofcrystallites of a metal oxide selected from the group consisting ofpalladium and rhodium oxide where the metal oxide has a crystallite sizesuch that the surface area is at least 0.75 m. /gm.; and

up to 35% by weight of a conductive component selected from the groupconsisting of silver, gold, and platinum where the cationratio of saidconductive component to said metal oxide component lies between 0.5 to1.5.

2. A metal glaze resistive composition adapted to be applied to andfired on a ceramic dielectric characterized by a microstructure having adispersion of metal oxide and metal in a glass matrix where the initialreaction mix for said metal glaze resistive composition includes:

40% to 60% by weight of vitreous enamel frit;

18% to 60% by weight of particles comprising agglomerates ofcrystallites of a metal oxide selected from the group consisting ofpalladium and rhodium oxide where the metal oxide has a crystallite sizesuch that the surface area is at least 0.75 m. /gm.; and

up to 22% by weight of a conductive component selected from the groupconsisting of silver, gold, and platinum where the cation ratio of saidconductive component to said metal oxide component lies between 0.9 to1.1.

3. A metal glaze resistive composition adapted to be applied to andfired on a ceramic dielectric characterized by a microstructure having adispersion of metal oxide and metal in a glass matrix where the initialreaction mix for said metal glaze resistive composition includes:

35 to 70% by weight of vitreous enamel frit;

up to 5% by Weight of a dispersing agent selected from the groupconsisting of the oxides of silicon and aluminum;

to 70% by weight of particles comprising agglomerates of crystallites ofa metal oxide selected from the group consisting of palladium andrhodium oxide where said oxide constituent has a crystallite size suchthat the surface area is at least 0.75 m. /gm.; and

up to 35 by weight of a conductive component selected from the groupconsisting of silver, gold and platinum where the cation ratio ofconductive component to said metal oxide component lies between 0.5 to1.5.

4. A metal glaze resistive composition adapted to be 10 applied to andfired on a ceramic dielectric characterized by a microstructure having adispersion of metal oxide and metal in a glass matrix where the initialreaction mix for said metal glaze resistive composition includes:

40% to 60% by weight of vitreous enamel frit;

1.6% to 4% by weight of a dispersing agent selected from the groupconsisting of the oxides of silicon and aluminum;

18% to 60% by weight of particles comprising agglomerates ofcrystallites of a metal oxide selected from the group consisting ofpalladium and rhodium oxide where said oxide constituent has acrystallite size such that the surface area is at least 0.75 m. /gm.;and,

up to 22% by weight of a conductive component selected from the groupconsisting of silver, gold and platinum where the cation ratioof'conductive component to said oxide component lies between 0.9 to 1.

5. An electrical resistor comprising a ceramic dielectric containing onthe surface thereof a metal glaze resistive element characterized by amicrostructure having a dispersion of metal oxide and metal in a glassmatrix where the initial reaction mix for said metal glaze resistivecomposition includes:

35% to 70% by weight of vitreous enamel frit;

up to 5% by weight of a dispersing agent selected from the groupconsisting of the oxides of silicon and aluminum;

15% to 7 0% by weight of particles comprising agglomerates ofcrystallites of a metal oxide selected from the group consisting ofpalladium and rhodium oxide where said oxide constituent is formed bysintering a member selected from the group consisting of palladium andrhodium crystallites having a size up to 1500 Angstroms; and,

up to 35% by weight of a conductive component selected from the groupconsisting of silver, gold and platinum where the cation ratio of saidconductive component to said oxide component lies between 0.5 to 1.5.

6. An electrical resistor comprising a ceramic containing on the surfacethereof a metal glaze resistive element characterized by amicrostructure having a dispersion of metal oxide and metal in a glassmatrix where the initial reaction mix for said metal glaze resistivecomposition includes:

40% to 60% by weight of vitreous enamel frit;

1.6% to 4% by weight of a dispersing agent selected from the groupconsisting of the oxides of silicon and aluminum;

18% to 60% by weight of particles comprising agglomerates ofcrystallites of a metal oxide selected from the group consisting ofpalladium and rhodium oxide where said oxide constituent is formed bysintering in an oxidizing atmosphere a member selected from the groupconsisting of palladium and rhodium crystallites having a size up to1500 Angstroms; and,

0 to 22% by weight of a conductive component selected from the groupconsisting of silver, gold and platinum where the cation ratio ofconductive component to said oxide component lies between 0.9 to 1.

7. A method for making an electrical resistor comprising the steps of:

heating a metal selected from the group consisting of palladium andrhodium in a nonoxidizing atmosphere to form metal crystallites withsize up to 1500 Angstroms;

sintering said metal crystallites in an oxidizing atmosphere to formsubstantially pure metal oxide particles comprising agglomerates ofcrystallites such that the surface area is at least 0.75 m. /gm.;

forming a reaction mixture with said metal oxide crystallites, saidreaction mixture consisting essentially of 35% to 70% by weight ofvitreous enamel frit, 15 to 70% by weight of said metal oxide and up to35% by weight of a conductive component se- 11 lected from the groupconsisting of silver, gold and platinum; applying said reaction mixtureto a ceramic surface;

and,

heating said reaction mixture to a temperature between about 750 C. to790 C. to form a metal glaze resistive element on said ceramic surfacecharacterized by a microstructure having a dispersion of metal oxide andmetal in a glass matrix.

8. The method of claim 7 wherein said reaction mixture additionallycontains a dispersing agent selected from the group consisting of theoxides of silicon and aluminum.

9. The method of claim 8 including the step of cooling said reactionmixture to room temperature to form an adherent metal-glaze resistive.elementon a ceramic surface.

v 10. The method of claim 9 wherein said reaction mixture consistsessentially of 40% to 60% by weight of vitreous enamel frit, up to 5% byWeight of said dispersing agent, and 18% to 60% by weight of said metaloxide.

11. A method for making an electrical resistor comprising the steps of:

heating a metal selected from the groupconsisting of palladium andrhodium, in a nonoxidizing atmosphere to form metal crystallites withsize up to 1500 Angstroms;

sintering said metal crystallites in an oxidizing atmosphere to formsubstantially pure metal oxide parti- 12 -cles comprising agglomeratesof crystallites such that the surface area is at least 0.75 mF/gms,forming a reaction mixture with said metal oxide crystallites, saidreaction mixture consisting essentially of to-% by weight of vitreousenamel frit, I 15% to 70% by weight of said metal oxide and up to 35% byweight of a conductive component selected from the group consisting ofsilver, gold and platinu-m; applying said reaction mixture to a ceramicsurface; firing said reaction mixture on said ceramic surface to atemperature of about 850 C. in an oxidizing atmosphere; a thereafterreoxidizing said fired reaction mixture at a temperature in the rangebetween 450 C. to 700 C.; and, I

cooling said mixture to form an adherent metal glaze resistive elementon a ceramic surface.

References Cited UNITED STATES PATENTS 3,052,573 9/1942 Dumesnil 117-227X 25 RALPH s. KENDALL, Primary Examiner.

ALFRED L. LEAVITT, Examiner.

E. B. LIPSCOMB III, Assistant Examiner.

